3 Basics | LXM32M |
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3.4Modbus services - "Function Code"
The table below provides an overview of the available Modbus serv- ices:
"Function | Meaning under Modbus | Meaning from device per- |
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3 | Read Multiple Registers | Reading a parameter |
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8 | Diagnostics | Diagnostics |
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16 | Write Multiple Registers | Writing a parameter |
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23 | Read/Write Multiple Registers | Reading and writing parame- |
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43 | Read Device Identification | – |
Subcode14 |
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90 | UMAS File Transfer (Upload) | – |
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3.4.1"Function Code" 3 (Read Multiple Registers)
This "Function Code" 3 (Read Multiple Registers) allows you to read several consecutive parameters, starting at any address.
Modbus request Structure of the Modbus request:
Field | Bytes | Value | Meaning |
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Function Code | 1 | 3 = 03h | Read Multiple Registers |
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Starting Address | 2 | (various) | Address of the first parameter to be read |
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Quantity Of Regis- | 2 | 2 * n | Number of 16 bit values to be read |
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Modbus response Structure of the positive Modbus response:
Field | Bytes | Value | Meaning | |
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Function Code | 1 | 3 | = 03h | Read Multiple Registers |
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Byte Count | 1 | 4 | * n | Number of data bytes |
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Registers Value | 4 * n | (various) | Parameter values | |
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Structure of the negative Modbus response
Field | Bytes | Value | Meaning |
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Function Code | 1 | 03h + 80h = 83h | Read Multiple Registers |
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Exception Code | 1 | 01h ... 04h | See chapter |
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| "3.3.2 Modbus response to a Modbus request" |
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0198441113843, V1.01, 01.2012
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